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Tunability is an important feature for the filter. As a special electromagnetic medium, the plasma has its permittivity being altered in a wideband range. In this work, based on the surface plasmon polaritons of plasma–dielectric–plasma waveguides, we propose a double-stubs structure submerged in a gaseous discharge plasma medium to realize tunable filtering properties in the giga-hertz (GHz) regime. The finite element method is applied to numerically compute filtering properties. The coupled mode theory and orthogonal design method are introduced to verify simulation results and estimate the effect of simulation parameters on the filtering properties. It is shown that the height of two stubs has the most important influence on filtering performance. Although once the filter is fabricated, its size cannot be modified, one can, nevertheless, vary the plasma frequency to effectively adjust the plasma frequency for the best filtering. Thus, such a plasma-modified filter provides a feasible scheme to dynamically adjust the filtering frequency.

In the giga-Hz (GHz) regime, not only does an advanced electromagnetic platform need a stealth function to shield itself from radar detection, similar to the “invisible” cloak in the visible light regime, but also an enhanced transmission function to communicate with others. To satisfy the seemingly contradictory requirements, we here propose a multi-functional mode of plasma cloaking, invisible to radar detection but signal-enhanced in communication bands. Such a synergistic effect is achieved by combining a “detour” layer of cloaking and an enhancement layer of communication. Thus, with such a design we can successfully apply an ideal “cloak” to the low frequency detecting regime (in the P-band) and improve signal transmission capabilities in a higher frequency communication regime (in the L-band) at the same time. Furthermore, the tunability and limitations of the multi-functional system are discussed, and the principles of designing inner and outer plasma layers are acquired.

In recent years, an innovative technology based on modulation and enhancement effects of subwavelength plasma on RF electromagnetic radiation has been proposed, in which the microwave radiation from an electrically small antenna can be significantly enhanced when the antenna is tightly enclosed by a subwavelength overdense plasma shell. But the exact mechanism is still not entirely clear. In this paper, we first use the theory of hybridized Local Surface Plasmon Resonance (LSPR) for visible light in nanometal to explain this cross-domain work of microwave radiation enhancement modulated by a subwavelength overdense plasma layer, and the results show that the LSPR frequency is in good accordance with the frequency of enhanced radiation signals. Furthermore, the relationship between LSPR and antenna impedance as well as their effects on the impedance matching condition between antenna and power supply are investigated. It is indicated that LSPR on the plasma layer changes the impedance of the antenna, which produces circuit resonance (differing from plasmon resonance) between the antenna and power supply, and thus more power is radiated from the power supply to free space.

The effects of A-site cation size mismatch on La0.7 − xNdxCa0.3 − y(Ba,Sr)yMnO3 perovskite materials with a constant A-site average ionic radius ⟨rA⟩ = 1.2052 A have been investigated. Polycrystalline samples have been prepared through the standard solid-state reaction method at high temperatures, and their structures, magnetic properties, and magnetocaloric effect (MCE) have been investigated in detail. X-ray diffraction patterns show that all of the samples crystallized in an orthorhombic structure with the space group Pnma. XPS analysis confirmed the Mn3+/Mn4+ ratio remained constant as σ2 was varied. Meanwhile, upon increasing σ2 from 0.0002 to 0.007, the Curie temperature (TC) decreased linearly from 254 K to 108 K. Based on M-H isotherms, Arrott plots and the maximum magnetic entropy prove a crossover of first-to-second-order transition with increasing σ2. Samples with σ2 = 0.0002, 0.001, and 0.003 exhibited a first-order transition and had larger MCEs than those showing a second-order transition.